The present invention relates to a variable valve system for an internal combustion engine, which is capable of varying and adjusting at least a valve lift amount of an engine intake valve or an engine exhaust valve in accordance with an engine operating state.
In recent years, there have been proposed and developed various variable valve systems, which control valve open and closure timings and a valve lift amount of engine intake/exhaust valves in accordance with an engine operating state in order to ensure an improvement of fuel efficiency and a stable drivability during an engine low-speed (low-revs) and low-load operation and to ensure a sufficient output by an increase of an intake air charging efficiency during an engine high-speed (high-revs) and high-load operation. One such variable valve system has been disclosed in Japanese Patent Provisional Publication No. 11-264307 (FIGS. 9 and 10) (hereinafter is referred to as “JP11-264307”) which was previously applied by the same applicants of this application.
Brief explanation of JP11-264307 will be made below. The variable valve system in JP11-264307 has a drive cam integrally formed with an outer circumference of a drive shaft that rotates by a crank shaft, a multi-link type transmission mechanism formed from a rocker arm that converts a turning force or torque of the drive cam into a rocking motion and a link member etc., a rockable cam that operates open/close function of an intake valve by its sliding motion on an upper surface of a valve lifter through the transmission mechanism, a support arm which is laying almost sideways and whose base end portion is rotatably supported by the drive shaft and whose top end portion is rotatably supported by a rocking fulcrum of the rocker arm of the transmission mechanism, a drive mechanism which revolves the top end side of the support arm in an up-and-down direction then inclines the support arm within a predetermined range, and a controller that controls a forward/reverse rotation of the drive mechanism in accordance with the engine operating state.
By controlling the revolution of the support arm in the up-and-down direction through the drive mechanism, a sliding position of the rockable cam on the upper surface of the valve lifter is changed via the rocker arm of the transmission mechanism and the link member, the lift amount of the intake valve is then controlled.